Glutamate Uncaging

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One of the first glutamate uncaging (p-hydroxyphenacyl-glutamate) experiments on dendrites was done by Kandler (1998) on CA1 pyramidal neurons in slices [1]. They reported the long-term depression of glutamate responses after the pairing of uncaging with depolarization of the neuron. A similar result was obtained with bursts of uncaging by Dodt (1999); these authors used an infrared-guided laser stimulation system to uncage glutamate on the apical dendrites of layer 5 neocortical pyramidal neurons.


The traditional uncaging groups, such as nitrobenzyls, are designed for one-photon uncaging.

Newer caged glutamate compounds have been designed for 2-photon uncaging. Furuta (1999) designed a bromo-hydroxycoumarin-caged compound (Bhc-glutamate) that is more than an order of magnitude more sensitive than carboxynitrobenzyl-glutamate (CNB-glutamate). The synthesis of Bhc-glutamate allowed the creation of three-dimensional maps of the glutamate sensitivity of pyramidal neurons in brain slices.



Uncaging Compounds

RuBi-Glutamate

  • caged-glutamate compound
  • based on ruthenium photochemistry
  • excited with visible wavelengths
  • releases glutamate after 1-photon or 2-photon excitation.
  • high quantum efficiency
  • can be used at low concentrations,
  • partly avoids blockade of GABAergic transmission
  • 2-photon uncaging of RuBi-Glutamate has a high spatial resolution and generates excitatory responses in individual dendritic spines with physiological kinetics.
  • With laser beam multiplexing, two-photon RuBi-Glutamate uncaging can also be used to depolarize and fire pyramidal neurons with single-cell resolution.
  • RuBi-Glutamate enables the photoactivation of neuronal dendrites and circuits with visible or two-photon light sources, achieving single cell, or even single spine, precision.

ruthenium-bipyridine complexes can be used as caging compounds. ruthenium is a transition metal with versatile chemistry. polypyridines of ruthenium photorelease entire ligands in a heterolytic fashion, by means of a widely known mechanism in which the initial photoexcited state quickly evolves into a dissociative state, so the photorelease is therefore clean and fast.


Pros: RuBi-Glutamate
  • minimal antagonistic effects on GABAergic transmission


Cons: RuBi-Glutamate
  • not much prior literature to demo the effects



MNI-Glutamate

2-photon uncaging of MNI-glutamate has been used successfully to functionally map synaptic receptors [2][3][4][5][6], activate individual spines, and individual neurons.

Two-photon excitation was used to uncage MNI-glutamate while measuring the resulting inward currents at the neuron’s cell body. This method resulted in an incredibly high-resolution view of the dendritic sites that were most sensitive to glutamate. Even the responses of single dendritic spines could be resolved. The pseudocoloring over the dendritic outline corresponds to the magnitude of the inward currents measured, as indicated by the colored scale bar below. [7]
Pros: MNI-glutamate
  • lots of prior literature to demo the effects
  • antagonist of GABAergic transmission at high concentrations


Cons: MNI-glutamate
  • needs to be applied to the tissue at relatively high (mM) concentrations for effective 2-photon uncaging.
  • antagonist to GABAergic transmission so can't be used to study GABAergic neurons




CNB-glutamate

CNB-glutamate



L-glutamic acid

L-glutamic acid α(4,5-dimethoxy-2-nitrobenzyl) ester (Callaway, Katz, 1993)



REFERENCES

<references>

[1]

[2]


[3]


[4]


[5]


[6]

[7]


  1. 1.0 1.1 Kandler, Katz, Kauer 1998 Focal photolysis of caged glutamate produces long-term depression of hippocampal glutamate receptors
  2. 2.0 2.1 Araya Yuste 2006 The spine neck filters membrane potentials
  3. 3.0 3.1 Carter Sabatini 2004 State-dependent calcium signaling in dendritic spines of striatal medium spiny neurons
  4. 4.0 4.1 Gasparini Magee 2006 State dependent dendritic computation in hippocampal CA1 pyramidal neurons
  5. 5.0 5.1 Matsuzaki Kasai 2001 Dendritic spine geometry is critical for AMPA receptor expression in hippocampal CA1 pyramidal neurons
  6. 6.0 6.1 Sobczyk Svoboda 2005 NMDA receptor subunitdependent Ca2 signaling in individual hippocampal dendritic spines
  7. 7.0 7.1 Callaway Yuste 2002 Stimulating neurons with light


  • Salierno Marceca Peterka Yuste Etchenique 2010 fast ruthenium polypyridine cage complex photoreleases glutamate with visible or IR light in one and two photon regimes J Inorg Biochem
  • Callaway Katz 1993 Photostimulation using caged glutamate reveals functional circuitry in living brain slices
  • Frick Dodt 2001 Glutamate receptors form hot spots on apical dendrites of neocortical pyramidal neurons
  • Pettit Augustine 1997 Chemical twophoton uncaging: a novel approach to mapping glutamate receptors
  • Shepherd Svoboda 2003 Circuit analysis of experience-dependent plasticity in the developing rat barrel cortex
  • Wieboldt Hess 1994 Photolabile precursors of glutamate: synthesis, photochemical properties, and activation of glutamate receptors on a microsecond time scale.
  • Yoshimura Callaway 2005 Excitatory cortical neurons form fine-scale functional networks.